全文获取类型
收费全文 | 128202篇 |
免费 | 10272篇 |
国内免费 | 8722篇 |
专业分类
电工技术 | 5765篇 |
技术理论 | 73篇 |
综合类 | 13089篇 |
化学工业 | 21371篇 |
金属工艺 | 2493篇 |
机械仪表 | 4454篇 |
建筑科学 | 28253篇 |
矿业工程 | 6598篇 |
能源动力 | 6309篇 |
轻工业 | 5760篇 |
水利工程 | 20322篇 |
石油天然气 | 8668篇 |
武器工业 | 930篇 |
无线电 | 3111篇 |
一般工业技术 | 7918篇 |
冶金工业 | 4167篇 |
原子能技术 | 1252篇 |
自动化技术 | 6663篇 |
出版年
2024年 | 235篇 |
2023年 | 1532篇 |
2022年 | 2568篇 |
2021年 | 3476篇 |
2020年 | 3685篇 |
2019年 | 3003篇 |
2018年 | 2886篇 |
2017年 | 3521篇 |
2016年 | 4122篇 |
2015年 | 4192篇 |
2014年 | 8991篇 |
2013年 | 7821篇 |
2012年 | 9618篇 |
2011年 | 9796篇 |
2010年 | 7577篇 |
2009年 | 7880篇 |
2008年 | 7245篇 |
2007年 | 9280篇 |
2006年 | 8527篇 |
2005年 | 7789篇 |
2004年 | 6358篇 |
2003年 | 5413篇 |
2002年 | 4449篇 |
2001年 | 3547篇 |
2000年 | 2977篇 |
1999年 | 2281篇 |
1998年 | 1644篇 |
1997年 | 1368篇 |
1996年 | 1045篇 |
1995年 | 954篇 |
1994年 | 707篇 |
1993年 | 550篇 |
1992年 | 445篇 |
1991年 | 314篇 |
1990年 | 235篇 |
1989年 | 239篇 |
1988年 | 154篇 |
1987年 | 154篇 |
1986年 | 112篇 |
1985年 | 117篇 |
1984年 | 119篇 |
1983年 | 72篇 |
1982年 | 42篇 |
1981年 | 19篇 |
1980年 | 30篇 |
1979年 | 24篇 |
1977年 | 11篇 |
1961年 | 6篇 |
1957年 | 6篇 |
1951年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
The present study was conducted to develop subcritical water extraction (SWE) of Echinacea purpurea flowers. The influence of temperature and extraction time on quality of extracts considering total phenols content, total flavonoids content, antioxidant capacity and extraction yield, was determined. Optimized extraction parameters for maximised investigated responses were as follows: 147.56 °C and 8.43 min. The experimental values agreed with the values predicted, thus indicating the adequacy of central composite experimental design for modelling the SWE of bioactive compounds from E. purpurea. Results of the study also highlighted the potential application of E. purpurea subcritical water extracts as a source of valuable bioactive compounds. 相似文献
52.
《石油化工》2015,44(4):506
采用便携式微量水分析仪和库仑法微量水分析仪测定了乙烯、丙烯试样中的微量水含量,对试样的传输系统、进样量的控制、液体试样的气化和水标准气体的制备方法进行了改进,优化了测试条件。以低吸附惰性管线和小死体积单进单出的不锈钢减压器为试样传输系统,缩短了测试时间。采用液态烃闪蒸气化取样进样器气化液体试样并准确控制试样的进样量,可避免液体试样渐次气化对水含量测定结果的影响及对采样钢瓶大小的限制。采用渗透管发生器制备水标准气体,可验证分析结果的准确度。采用库仑法微量水分析仪测定水含量时,试样流量选择600 m L/min较适宜,开封保存15 d之内的卡尔·费休试剂对测定结果无影响。采用便携式微量水分析仪测定水含量时,选择试样流量在400~800 m L/min之间较适宜。两种仪器的测量结果相近,稳定性好,准确度高,回收率在102%~107%之间,相对偏差小于10%。 相似文献
53.
文章通过对黑龙江省高效节水现状,存在问题的分析,结合黑龙江省高效节水发展的支撑能力,阐述黑龙江省节水增粮目标、任务及总体布局,为黑龙江省2012—2015年节水增粮实施提供依据。 相似文献
54.
55.
Data fitting with B-splines is a challenging problem in reverse engineering for CAD/CAM, virtual reality, data visualization, and many other fields. It is well-known that the fitting improves greatly if knots are considered as free variables. This leads, however, to a very difficult multimodal and multivariate continuous nonlinear optimization problem, the so-called knot adjustment problem. In this context, the present paper introduces an adapted elitist clonal selection algorithm for automatic knot adjustment of B-spline curves. Given a set of noisy data points, our method determines the number and location of knots automatically in order to obtain an extremely accurate fitting of data. In addition, our method minimizes the number of parameters required for this task. Our approach performs very well and in a fully automatic way even for the cases of underlying functions requiring identical multiple knots, such as functions with discontinuities and cusps. To evaluate its performance, it has been applied to three challenging test functions, and results have been compared with those from other alternative methods based on AIS and genetic algorithms. Our experimental results show that our proposal outperforms previous approaches in terms of accuracy and flexibility. Some other issues such as the parameter tuning, the complexity of the algorithm, and the CPU runtime are also discussed. 相似文献
56.
Combination of heat treatment and chitosan coating to improve postharvest quality of wolfberry (Lycium barbarum) 下载免费PDF全文
Zhaojun Ban Wenwen Wei Xiangzheng Yang Jianhua Feng Junfeng Guan Li Li 《International Journal of Food Science & Technology》2015,50(4):1019-1025
The synergistic application of hot water dip at 42 °C for 30 min and 1% chitosan coating on differentiation in postharvest quality traits, microstructure as well as microbiological evolution of wolfberry fruits was investigated. Fresh wolfberry fruits were stored at 2 ± 0.5 °C and 90% relative humidity (RH) for 28 days. Results indicated the combination of prestorage heat treatment and chitosan coating maintained higher levels of ascorbic acid, total phenolic contents and antioxidant capacity as well as lower decay, compared with untreated wolfberry fruits. The possible mechanism was that the heat treatment almost sealed open stomata to limit the sites of pathogen penetration into fruits independently, followed by the biofilm formed by chitosan which controlled secondary infections as well as slowed changes in fruit respiration and metabolic activity in wolfberries. The synergistically treated fruit also exhibited a higher acceptability obtained by sensory analysis after cold storage. In this sense, the integrated application of heat treatment and chitosan coating could be regarded as an effective strategy to extend storage life and maintain the postharvest quality of wolfberry fruits. 相似文献
57.
58.
Bo Wang Edison Huixiang Ang Yang Yang Yufei Zhang Hongbo Geng Minghui Ye Cheng Chao Li 《Advanced functional materials》2020,30(28)
Orthorhombic molybdenum trioxide (MoO3) is one of the most promising anode materials for sodium‐ion batteries because of its rich chemistry associated with multiple valence states and intriguing layered structure. However, MoO3 still suffers from the low rate capability and poor cycle induced by pulverization during de/sodiation. An ingenious two‐step synthesis strategy to fine tune the layer structure of MoO3 targeting stable and fast sodium ionic diffusion channels is reported here. By integrating partially reduction and organic molecule intercalation methodologies, the interlayer spacing of MoO3 is remarkably enlarged to 10.40 Å and the layer structural integration are reinforced by dimercapto groups of bismuththiol molecules. Comprehensive characterizations and density functional theory calculations prove that the intercalated bismuththiol (DMcT) molecules substantially enhanced electronic conductivity and effectively shield the electrostatic interaction between Na+ and the MoO3 host by conjugated double bond, resulting in improved Na+ insertion/extraction kinetics. Benefiting from these features, the newly devised layered MoO3 electrode achieves excellent long‐term cycling stability and outstanding rate performance. These achievements are of vital significance for the preparation of sodium‐ion battery anode materials with high‐rate capability and long cycling life using intercalation chemistry. 相似文献
59.
在分析传统单片机教学存在问题的基础上,提出面向工程应用,聚焦企业需要,构建能力递进、面向应用的内容体系,搭建资源共享、实践创新、师生互动的自主学习平台,组建培养兴趣,突出技能的“双师型”教学团队,实践表明,在传授知识的同时,能有效提升学习兴趣,优化人才素质结构。 相似文献
60.
随着社会的不断发展,矿产资源为我国带来了巨大的经济效益,并在社会经济发展中占有重要的地位。但在矿山资源开发的过程中,威胁人身安全的事故经常发生。因此,本文对探矿工程安全措施进行了研究和分析。 相似文献